It is necessary for magnetic resonance tomography (MR) to detect the ECG signals of the patients in order to synchronize the triggering of the MR measuring sequences to the heart beat of the patient. Likewise, the ECG signal detected during an MR examination allows the information about the current heart phase to be acquired. If the ECG signals and the triggering of the measuring sequence are not synchronized, there is a danger that the MR images contain movement artifacts.
In practice however there are difficulties associated with the detection of the ECG signals, since the electrical and magnetic fields acting during the MR sequences significantly interfere in the ECG electronics circuit, whereby the reliable determination of the heart phase is impaired. Aside from these undesired interferences in the ECG electronics circuit, the so-called magnetohydrodynamic effect occurs in the case of a higher magnetic fluid densities, which results in a superelevation of the T wave of the heart beat. The different phases of the heart cycle are indicated in the electrocardiography using letters, for instance by the sequence P-Q-R-S-T. Here the R wave shows the greatest deflection. It is the center of reference of the triggering and must therefore be reliably determined.
A method for ECG triggering a measuring sequence in a magnetic resonance device is known from U.S. Pat. No. 6,070,097. However, the ECG signals of a patient are detected there via a single channel.
The detection of two ECG channels has been proposed in WO 99/04688, a vector display in a coordinate system being derived therefrom. The R wave of the heart cycle should be able to be taken from this display. It is however doubtful whether this method is satisfactorily reliable as this vector projection is dependent on many influences, for instance it changes if the patient holds his/her breath.